In modern and future (cellular) communication systems, an inter-band multi-carrier capability of devices such as terminal devices is gaining more attention and importance.
For example, in 3GPP systems, inter-band carrier aggregation represents an inter-band multi-carrier communication framework which shall be supported by devices such as terminal devices. In inter-band carrier aggregation, at least two carriers operating on different (frequency) bands are aggregated together in/for at least one of downlink and uplink.
Typically, any inter-band multi-carrier capable devices are operable both in a carrier combination/aggregation transmission mode and a single carrier transmission mode, respectively.
When multiple carriers operating on different (frequency) bands are combined or aggregated (which is regarded as a carrier combination/aggregation transmission mode herein), such as in inter-band carrier aggregation, intermodulation distortion (IMD) is typically produced due to nonlinearity in active and/or passive components of a device transmitter (in case of uplink transmission), a device receiver (in case of downlink transmission) or a device transceiver (in both cases). Generally, intermodulation distortion components of (m+n)-th order are located at frequencies m*f1±*f2. For instance, assuming that uplink carriers at frequencies fUL1 and fUL2 are combined or aggregated, a second order intermodulation distortion component is located at one of frequencies 2*fUL1, 2*fUL2, and fUL1±fUL2, and a third order intermodulation component is located at one of frequencies 3*fUL1, 3*fUL2, 2*fUL1±fUL2, fUL1±2*fUL2, and so on.
When at least one (or part) of the intermodulation distortion components falls in a (frequency) band being used for some transmission operation by the device in question, e.g. a DL carrier, such intermodulation distortion can cause a significant amount of desensitization. Such desensitization is specifically applicable for certain (inter-hand) combinations of standardized carriers depending on the frequency relations between uplink and downlink channel definitions.
Namely, for certain frequency relations between uplink and downlink channel definitions, (part of) intermodulation distortion components of uplink carrier combinations hit on top of a downlink carrier and thus destroy the performance thereof, if no additional power restrictions are in place. Referring to 3GPP uplink and downlink channel definitions according to 3GPP TS 36.104 (Table 5.5-1), for example, aggregating bands (i.e. aggregating component carriers operating on bands) B20 and B8 causes a third order intermodulation distortion component from B20 UL (832-862 MHz) and B8 UL (880-915 MHz) to overlap with B8 DL (925-960 MHz). Furthermore, (part of) intermodulation distortion components can also hit on top of some non-3GPP Radio Access Technology (RAT), for instance in the 2.4 GHz frequency band (ISM band) used e.g. by WLAN and Bluetooth. For instance, this is the case for the second order intermodulation distortion component when aggregating bands B4 and B12.
The intermodulation problem as outlined above, i.e. an excessive desensitization of some operating band/carrier (e.g. a DL carrier in case of a multi-band UL carrier combination), can be avoided if the intermodulation power of an intermodulation distortion component is sufficiently low so as compared with the actual transmission power of that operating band/carrier. For instance, desensitization could be considered to be not significant when being smaller than 0.5 dB.
However, there are currently no means for reliably and efficiently ensuring such sufficiently low level of desensitization in the context of intermodulation distortion for inter-band multi-carrier combinations or aggregations, particularly while avoiding coverage problems.
Namely, using band-specific power restriction values such as A-MPR is not effective for inter-band multi-carrier combinations or aggregations. On the one hand, specifying appropriate A-MPR values for all involved bands in all conceivable band/carrier combinations in a reliable manner is not easily feasible or at least cumbersome. On the other hand, even if so, separate power control of individual bands/carriers to be combined may lead to unnecessary or excessive reduction in coverage of the respective uplink/downlink transmissions for avoiding excessive desensitization.
Accordingly, there may be a case where operation in the carrier combination/aggregation transmission mode is not feasible or practicable in terms of requirements on coverage and/or transmission performance, etc.
Otherwise, there may be a case where a device operates in the single carrier transmission mode, although an operation in the carrier combination/aggregation transmission mode might be feasible or practicable in terms of requirements on coverage and/or transmission performance, etc. In such case, the device would waste resources or capabilities in terms of coverage and/or transmission performance, etc.
Thus, there is a desire to provide for transmission mode control for inter-band multi-carrier capable devices. More specifically, is a desire to provide for transmission mode control for inter-band multi-carrier capable devices in terms of at least one of coverage and control flexibility, e.g. in the context of inter-band carrier aggregation.